Can you kill units and save them with Soraka to pay the equip cost for Blade of the Ruined King?

Question

Accepted Answer

Yes. Paying the Equip cost on Blade of the Ruined King that says “Kill a friendly unit” counts as paid even if a replacement effect (for example, Soraka’s effect) prevents or replaces that unit’s death. Replacement effects that change the outcome of a cost do not stop the cost from being considered paid [357.2.a].

You may pay Blade of the Ruined King’s Equip cost by killing a friendly unit and, if Soraka’s replacement effect replaces that death (e.g., heals or returns the unit instead), the kill cost is still considered paid and the Equip activation can continue [357.2.a]. If the result of the replacement makes attaching illegal (for example, if the unit you attempted to attach to is no longer a legal attach target), the attachment step may fail in the usual way; if you are using a Weaponmaster shortcut to pay an Equip cost to attach to a unit being played, see Weaponmaster rules because the chosen Equip may remain where it was if its Equip cost can’t be paid or it can’t be attached to the intended unit [821.1.c.5] [821.1.c.2].

Begin activating Blade of the Ruined King’s Equip ability to attach it to a unit you control. Declare and perform the non-standard cost "Kill a friendly unit" as part of paying the Equip cost. If a replacement effect (for example, Soraka’s replacement) changes that death into something else (heal, return, etc.), that replacement occurs as part of paying the cost. Because the replacement changed the death, you nevertheless have paid the cost; the Equip activation continues and you pay remaining costs (Energy/Power) [357.2.a]. When the Equip ability resolves, attempt to Attach Blade of the Ruined King to the chosen unit. If the chosen attach target is no longer legal, the attachment may fail as it would for any other illegal attach target; if using Weaponmaster to attach at play, see Weaponmaster exceptions [821.1.c.2] [821.1.c.5].

If Soraka’s effect is not a replacement effect but instead prevents damage that would have killed the unit, whether the Equip cost was actually "paid" depends on the exact wording. The ruling above assumes a replacement-of-death effect; without the exact Soraka text we cannot be certain. If you tried to kill the same unit you intend to attach the Equipment to, and a replacement effect prevents that unit’s death but also renders it an illegal attach target (for instance, it is no longer 'a unit you control' or is in an unexpected zone), the attachment can fail. If you used a Weaponmaster shortcut when playing a unit, Weaponmaster rules say the Equip may remain where it was if the Equip cost can’t be paid or attachment isn’t possible [821.1.c.5]. If the Equip cost’s kill instruction required choosing a target in wording that would target (not typical for 'Kill a friendly unit'), Deflect or targeting restrictions could matter; the Equip cost as printed here is a cost within instructions and does not target per the cost-within-instructions rule [355.10.c.1]. If paying the cost would deterministically make the Equip activation illegal later (and you had a different legal choice), you must avoid making that illegal payment unless you had no choice, per cost-payment legality rules [357.3].

The key rule is that costs which are replaced by replacement effects are still considered paid. The Equip ability on Blade of the Ruined King has a non-standard cost: “Kill a friendly unit.” If you activate that Equip and perform the killing as the cost, a replacement effect that would replace or prevent that unit’s death (for example, a Soraka effect that replaces "would die" with "do X instead") does not undo the fact that you performed the cost — the cost is still treated as paid [357.2.a]. Costs embedded in instructions like “Kill a friendly unit” are costs within instructions and do not target in the targeting sense, so they are handled as costs rather than targeted effects [355.10.c.1]. After the replacement effect resolves, the Equip activation continues and you finish paying costs (Energy/Power) and resolving the Equip ability [357.2.a]. If, however, the replacement outcome makes the attach step illegal (for example, the chosen attach target is no longer a legal unit you control), the attachment can fail just as any attachment would when its target is illegal; if you were using Weaponmaster to pay an Equip cost when playing a unit, the Weaponmaster rules explain that if the chosen Equip’s Equip cost can’t be paid or it can’t be attached to the unit with Weaponmaster, it stays where it is [821.1.c.2] [821.1.c.5]. Because Soraka’s exact text was not provided, this explanation assumes her effect functions as a replacement of a death (similar to the Zhonya’s Hourglass example in the rules). If Soraka’s effect instead functions differently (for example, purely damage prevention that prevents the kill from ever being a death), the specifics could change; the broad principle from the rules is that replacement of a cost’s event still leaves the cost considered paid [357.2.a].